The present disclosure relates to a casing structure of an automotive internal combustion engine including an upper/lower divided crankcase structure.
In the upper/lower divided crankcase structure for an internal combustion engine, normally, an upper crankcase and a lower crankcase axially support a crankshaft and a transmission shaft of a transmission so as to be sandwiched at a dividing surface.
One known internal combustion engine has a general structure where the upper crankcase and lower crankcase axially support the crankshaft and a counter shaft of the transmission so as to be sandwiched at the dividing surface. The engine is installed in a vehicle so that the dividing surface forms a horizontal plane.
Further, the cylinder axial line of the cylinder formed on the upper crankcase is inclined to the transmission side so that the overall vertical dimension of the internal composition engine is kept small by inclining the cylinder, cylinder head, and cylinder cover that are sequentially overlaid upwardly.
In a known automotive internal combustion engine, a main shaft of a transmission is installed above and between the counter shaft and the crankshaft axially supported by the dividing surface of the upper crankcase and lower crankcase.
The transmission case portion of the upper crankcase bulges upward due to the main shaft and accessories and the like provided on the main shaft. Therefore, the incline of the cylinder axial line is restricted, thereby limiting the reduction in the overall vertical dimension of the internal combustion engine.
Further, the upper crankcase has a cylinder formed inclined relative to the dividing surface with the lower crankcase. Therefore, bolt holes must also be formed to incline relative to the dividing surface for bolts to integrally fasten the cylinder head laid over the cylinder. This increases the complexity of manufacturing the crankcase.